The present invention relates to a magnetic fluid sealer that employs magnetic fluids and a method for mounting the magnetic fluid sealer, which are applied to, for example, a light-shielding device such as one used in a zoom lens unit of a camera, in which light-shielding is performed by using magnetic fluids.
Conventionally, when a zoom lens unit of a camera or the like is subjected to light-shielding, a contact-type sealer that uses a contact-type sealing member such as silicon rubber is employed as a light-shielding device. Slide resistance of the contact-type shielding member of such a contact-type sealer is considerably small as compared with that of a normal oil sealing member.
However, as miniaturization and expansion in functionality of a camera have advanced in recent years, power saving of each of the units that compose the camera has become a problem. In order to reduce power consumption which is required at the time when a zoom lens is driven, the reduction of slide resistance with respect to a shielding member is further required.
However, in the conventional light-shielding device that employs the contact-type sealing member, sliding is effected by contact made between solids. As a result, there is a limitation inevitably placed on the extent of reduction in slide resistance of the contact-type sealing member.
Thus, the applicant has devised a light-shielding device which is a magnetic fluid sealer for conducting the light-shielding by using magnetic fluids as shown in FIG. 7.
The conventional light-shielding device that employs magnetic fluids will be described below with reference to FIG. 7. In FIG. 7, lens barrels 5 and 6 aligned as double barrels constitute a zoom lens unit of a compact camera, and a lens 7 and a shutter unit 8 are disposed inside the lens barrel 6.
A light-shielding device 1 includes a pair of annular magnets 2 and 3 which are mutually inversely polarized in the radial direction, and disposed in the inner peripheral face of the lens barrel 5 and a magnetic fluid 4 held in a gap between the inner peripheral face (magnetic pole) of the annular magnets 2 and 3 and the outer peripheral face of the lens barrel 6 by a magnetic circuit formed by the pair of annular magnets 2 and 3.
The light-shielding device 1 slides through the contact made between the magnetic fluid 4 and the lens barrel 6, that is, between a fluid and a solid, thereby remarkably reducing the slide resistance as compared with the conventional light-shielding device employing the contact-type shielding member.
However, in the above-described conventional technique, there is a problem as described below.
In the light-shielding device 1 that employs magnetic fluids as shown in FIG. 7, the surface of the magnetic fluid 4 is held substantially along the isomagnetic field lines of the spatial magnetic field that is generated by the pair of annular magnets 2 and 3.
Accordingly, even when the gap between the lens barrels 5 and 6 is changed due to eccentricity or the like, if the outer peripheral face of the lens barrel 6 remains within the area that is covered by the spatial magnetic field generated by the pair of annular magnets 2 and 3, and the surface of the magnetic fluid 4 is held substantially along the isomagnetic field lines that are in contact with the outer peripheral face of the lens barrel 6 (when the magnetic fluid 4 of the amount required for achieving the above is present), the magnetic fluid 4 is capable of completely light-shielding the gap between the lens barrels 5 and 6 as shown in FIG. 8.
However, when the maximum interval of the gap between the lens barrels 5 and 6 goes beyond the area that is covered by the spatial magnetic field generated by the pair of annular magnets 2 and 3, or when the magnetic fluid 4 of the amount sufficient to block the gap between the lens barrels 5 and 6 is not present, the magnetic fluid 4 cannot perform light-shielding with respect to the gap between the lens barrels 5 and 6 as shown in FIG. 9.
In order to avoid the state shown in FIG. 9 and to maintain the light-shielding property of the light-shielding device 1 even when the gap between the lens barrels 5 and 6 is changed due to eccentricity or the like, it is necessary that the pair of annular magnets 2 and 3 are changed to those that produce more intense magnetic force to elevate the intensity of the spatial magnetic field, or that the amount of the magnetic fluid 4 that is retained in the gap between the lens barrels 5 and 6 is increased. However, enlargement of the pair of annular magnets 2 and 3 is caused to produce an intense magnetic force, and when the amount of the magnetic fluid 4 is increased, the slide resistance is increased due to the increased contact area between the magnetic fluid 4 and the lens barrel 6. Therefore, these methods are not preferred.
The present invention has been made in view of the above problem inherent in the prior art. Accordingly, an object of the present invention is to provide a high-performance magnetic fluid sealer, which is capable of maintaining light-shielding property even when an interval change of a gap is large, and a method for easily mounting the magnetic fluid sealer.
The present invention adopts the following construction to solve the above problem.
In order to attain the above object, a magnetic fluid sealer of the present invention is a magnetic fluid sealer for preventing light leakage through a gap between two members mounted so as to be relatively movable with respect to each other, comprising: a magnetic circuit forming means which includes a magnetic force producing means for producing magnetic force and a pair of magnetic pole units opposing one of the two members, and forms a magnetic circuit that passes through the gap; and a magnetic fluid that is magnetically retained in the pair of magnetic pole units of the magnetic circuit forming means, which contacts with one of the above-mentioned members to thereby conduct light-shielding with respect to the gap, characterized in that the magnetic circuit forming means is provided so as to be relatively movable in response to an interval change of the gap.
Thus, even when the interval change of the gap between the two members is caused due to eccentricity or the like, the gap between the magnetic circuit forming means that retains the magnetic fluid and one of the two members can be kept constant. Thus, the area in which the magnetic fluid is in contact with one of the members is not enlarged, whereby the slide resistance of the magnetic fluid sealer can be always kept constant regardless of the eccentricity amount.
Accordingly, the light-shielding property can be maintained even in the case where the interval change of the gap is large, without enlarging a magnetic force producing means in response to the eccentricity amount to obtain increased magnetic force or increasing the amount of the magnetic fluid.
It is preferable that the magnetic circuit forming means is provided so as to be movable in a vertical direction with respect to the one of the two members, within a fitting groove that is provided in the other one of the two members.
Accordingly, the magnetic circuit forming means is supported by levitation from one of the members by magnetic levitation force which the magnetic fluid imparts in the fitting groove. Even in the eccentric state, the magnetic circuit forming means can radially move so as to keep a constant gap from one of the members with the magnetic fluid.
It is preferable that a leakage prevention member for preventing a leakage of the magnetic fluid in an axial direction is provided in at least one of the side surfaces of the magnetic circuit forming means in an axial direction.
Accordingly, a leakage of the magnetic fluid in an axial direction can be prevented by the leakage prevention member.
It is preferable that the surface of the one of the members is coated with a wettability reducing member for reducing wettability with the magnetic fluid.
Thus, the magnetic fluid that is in contact with one of the members can be prevented from wetting the surface of one of the members, thereby being capable of preventing reduction in the amount of the magnetic fluid that is retained in the magnetic pole units. As a result, light-shielding can be performed for a long period of time.
It is preferable that the magnetic circuit forming means is provided in a manner such that the pair of magnetic pole units are formed in a pair of the magnetic force producing means that are coupled while being mutually inversely polarized.
Thus, the magnetic circuit forming means may be simply constructed, thereby being excellent in its manufacturing property and assembling property.
It is preferable that the magnetic fluid sealer is disposed in a zoom lens unit of a camera.
Accordingly, the slide resistance of the zoom lens unit of a camera can be reduced, the power consumption amount that is required for performing zooming with the zoom lens unit or the like may also be reduced, thereby being capable of attaining power conservation of the camera. Also, the eccentricity following property of the zoom lens unit is enhanced to save space thereof, thereby being capable of achieving miniaturization of the camera.
It is a magnetic fluid sealer that is provided in a gap between two members mounted so as to be relatively movable with respect to each other, comprising:
a magnetic circuit forming means which includes a magnetic force producing means for producing magnetic force, and forms a magnetic circuit that passes through the gap; and
a magnetic fluid that is magnetically retained by magnetic flux passing through the gap of the magnetic circuit formed by the magnetic circuit forming means, which contacts with one of the two members to thereby seal the gap,
characterized in that:
the magnetic fluid sealer further comprises a sleeve mounted to the other one of the two members and in which a fitting groove is formed at the position opposing the one of the members; and
the magnetic circuit forming means is arranged in the fitting groove of the sleeve so as to be movable in a vertical direction with respect to the one of the members.
Therefore, the magnetic circuit forming means is supported by levitation from one of the members by magnetic levitation force which the magnetic fluid imparts in the fitting groove of the sleeve. Thus, even in the eccentric state, the magnetic circuit forming means can radially move so as to keep a constant gap from one of the members with the magnetic fluid.
Accordingly, the area in which the magnetic fluid is in contact with one of the members is not enlarged, and the slide resistance of the magnetic fluid sealer can be always kept constant regardless of the eccentricity amount, so that light-shielding property or dust-proof property can be maintained even in the case where the interval change of the gap is large.
It is preferable that a leakage prevention member for preventing a leakage of the magnetic fluid in an axial direction is provided in at least one of the side surfaces of the magnetic circuit forming means in an axial direction.
Accordingly, a leakage of the magnetic fluid in an axial direction can be prevented by the leakage prevention member. Further, entering of foreign materials into the magnetic fluid from the outside can be also securely prevented.
It is preferable that, when mounting the magnetic fluid sealer between the two members, the sleeve in which retaining of the magnetic fluid and disposing of the magnetic circuit forming means into the fitting groove have been completed is mounted in advance to a jig having a magnetic fluid contact portion whose surface configuration is substantially the same as that of the one of the members, and the sleeve is slid to amounting portion of the two members while making an end portion of the magnetic fluid contact portion of the jig be opposed to an end portion of the one of the members, to thereby mount it to the other one of the members.
Thus, prior to mounting to the mounting portion of the two members, the magnetic fluid can be filled in advance. Then, mounting can be effected by simply sliding the sleeve to the mounting portion, thereby achieving excellent mounting operability. Also, the manufacturer of the magnetic fluid sealer can fill magnetic fluids in advance before shipping the magnetic fluid sealer, so that the manufacturer of the magnetic fluid sealer can manage the filling amount of magnetic fluids.
It is preferable that the surface of the magnetic fluid contact portion of the jig remains in the state in which its wettability with magnetic fluids has been reduced.
Accordingly, adherence of magnetic fluids with respect to the magnetic fluid contact portion of the jig can be reduced, thereby being capable of strict managing the filling amount of magnetic fluids before performing the mounting.
It is preferable that the magnetic circuit forming means is provided in a manner such that the pair of magnetic pole units are formed in a pair of the magnetic force producing means that are coupled while being mutually inversely polarized in a vertical direction with respect to the one of the members.
Therefore, the magnetic circuit forming means may be simply constructed, thereby being excellent in its manufacturing property and assembling property, while at the same time being capable of producing intense magnetic force.
A method for mounting a magnetic fluid sealer of the present invention is a method of mounting a magnetic fluid sealer between two members, the magnetic fluid sealer that is provided in a gap between the two members mounted so as to be relatively movable with respect to each other and comprising: a magnetic circuit forming means which includes a magnetic force producing means for producing magnetic force and forms a magnetic circuit that passes through the gap; a magnetic fluid that is magnetically retained by magnetic flux passing through the gap of the magnetic circuit formed by the magnetic circuit forming means, which contacts with one of the two members to thereby seal the gap; and a sleeve mounted to the other one of the two members and in which the the magnetic circuit forming means is disposed, characterized by comprising:
mounting in advance the sleeve in which retaining of the magnetic fluid and disposing of the magnetic circuit forming means have been completed, to a jig having a magnetic fluid contact portion whose surface configuration is substantially the same as that of the one of the members; and
sliding the sleeve to a mounting portion of the two members while making an end portion of the magnetic fluid contact portion of the jig be opposed to an end portion of the one of the members, to thereby mount it to the other one of the members.
Accordingly, prior to mounting to the mounting portion of the two members, the magnetic fluid can be filled in advance. Then, mounting can be effected by simply sliding the sleeve to the mounting portion, thereby achieving excellent mounting operability. Also, the manufacturer of the magnetic fluid sealer can fill magnetic fluids in advance before shipping the magnetic fluid sealer, so that the manufacturer of the magnetic fluid sealer can manage the filling amount of magnetic fluids.
It is preferable that the surface of the magnetic fluid contact portion of the jig remains in the state in which its wettability with magnetic fluids has been reduced.
Accordingly, adherence of magnetic fluids with respect to the magnetic fluid contact portion of the jig can be reduced, thereby being capable of strict managing the filling amount of magnetic fluids before performing the mounting.
It is preferable that a fitting groove is formed in the sleeve at a position opposing the one of the members and that the magnetic circuit forming means is arranged in the fitting groove of the sleeve so as to be movable in a vertical direction with respect to the one of the members.
Therefore, the magnetic circuit forming means is supported by levitation from one of the members by magnetic levitation force which the magnetic fluid imparts in the fitting groove of the sleeve. Thus, even in the eccentric state, the magnetic circuit forming means can radially move so as to keep a constant gap from one of the members with the magnetic fluid.
Thus, the area in which the magnetic fluid is in contact with one of the members is not enlarged, and the slide resistance of the magnetic fluid sealer can be always kept constant regardless of the eccentricity amount, so that light-shielding property or dust-proof property can be maintained even in the case where the interval change of the gap is large.
It is preferable that a leakage prevention member for preventing a leakage of the magnetic fluid in an axial direction is provided in at least one of the side surfaces of the magnetic circuit forming means in an axial direction.
Therefore, a leakage of the magnetic fluid in an axial direction can be prevented by the leakage prevention member. Further, entering of foreign materials into the magnetic fluid from the outside can be also securely prevented.